1. Field of the Invention
The present invention relates to heat exchangers and, more particularly, to heat exchangers such as engine cooling radiators, charge air coolers, condensers, and the like, in which high stresses in the area of the tube-to-header joint due to temperature fluctuations lead to failure at or below the tube-to-header joint.
2. Description of Related Art
Heat exchangers such as engine cooling radiators, charge air coolers, oil coolers, and the like, typically consist of an inlet tank (or manifold) and an outlet tank (or manifold); a core section between the tanks with inlet and outlet headers connected to the tanks and with multiple fluid tubes running from the inlet header to the outlet header, with cooling fins attached between the tubes; and structural side pieces, one on each side, connected to the inlet and outlet tanks. These side pieces often provide attachments for mounting the heat exchanger.
Each of the fluid tubes is inserted into an opening in the wall of the inlet and outlet headers, respectively, and sealed to form a tube-to-header joint. During operation of the heat exchanger, the fluid-carrying tubes are subject to repeated expansion and contraction as the tubes are alternately heated and cooled, resulting in great stress in the area of the tube-to-header joints as the expanding and contracting tubes try to move the inlet and outlet headers, which are connected to the inlet and outlet tanks, which are restrained from movement by the structural side pieces.
As a result of the expanding and contracting tubes trying to move the immovable headers and tanks, the number one cause of failure of heat exchangers in service is failure of the outer tube-to-header joints or of the tubes adjacent to these joints. Much design effort has been expended in attempts to solve this problem, with examples including heat exchangers with resilient tube-to-header joints which provide sealing between the tubes and headers but allow for relative motion between the two without the build-up of high stresses. Some heat exchanger designs use special grommets in the tube-to-header joint, while others have included headers with molded silicone rubber connecting the header plate to metal inserts which become soldered to the tubes. Another approach to the problem has been to seal the tubes to the headers with molded-in-place room temperature vulcanization (RTV) silicone rubber, which provides both sealing and resiliency. All of these approaches add considerable cost to the heat exchanger over the cost of standard rigid tube-to-header joints.
Therefore, a need exists for a means to prevent end tube-to-header failures with a minimum expenditure of cost, material and labor, while preserving heat exchanger thermal performance.